Star Trek and any specific book or movie or whatever being "hard" sci fi is in the eye of the beholder.
To an extent, but "hard SF" is a specific sub-genre just like military SF, science fantasy or hard-boiled detective stories. Perhaps you hadn't heard the term before and mistook it for "real" or "good"?
The definition/restriction in this post is total snobby BS.
The snobbery is in your mind. When I want to read a hard-boiled detective story I reach for Mickey Spillane not C. J. Cherryh. For hard SF I'd recommend Robert L. Forward but not the excellent science fantasy of Sharon Lee and Steve Miller. Because they write in a different sub-genre.
Speculative fiction pushes boundaries of theory, wonder, reality and perception into new and interesting places, times and situations. If one were to accept this, then there would be no sci fi genre; it would merely be fiction relative to present-day science.
You're saying there is no real difference between Mexican, Chinese or Indian cuisine. "All food is food, relative to cooked organic matter and spices."
The laws of physics and other sciences aren't static and neither should our adventures in thinking about the future be.
"In this house we obey the laws of thermodynamics!" - H. Simpson
Our
understanding of the laws of nature might change but the laws themselves do not.
Anyway, the OP was asking for tacos instead of cannelloni, not attacking Star Trek.